Thiazolium‐Based Catalysts for the Etherification of Benzylic Alcohols under Solvent‐Free Conditions

Abstract

Thiazolium and imidazolium hybrid materials were prepared by radical reactions between a mercaptopropyl-modified SBA-15 mesoporous silica and bis-vinylthiazolium or bis-vinylimidazolium dibromide salts. These hybrid materials were characterized by several techniques and were employed in the etherification reaction of 1-phenylethanol. Solvent-free conditions at 160 8C under different gas phases (oxygen, air, nitrogen and argon) were used. The thiazolium-based material displayed excellent performances. Further studies were carried out using unsupported thiazolium salts, with or without a methyl group at the C-2 position of the thiazolium moiety. These studies allowed us to propose a reaction mechanism. The supported thiazolium-based material was successfully used in the etherification reaction of two other benzylic alcohols and also in seven consecutive cycles. This work represents the first use of thiazolium-based compounds as catalysts for the etherification reaction of alcohols.Scheme 1. Synthesis of SBA-15-Imi and SBA-15-Thia.

Cross‐Linked Thiazolidine Network as Support for Palladium: A New Catalyst for Suzuki and Heck Reactions

“…Elemental analysis gave a thiazolium loading of 2.28 mmol g −1 . These data are comparable with those of a previous synthesis of the same material 15…”

“…In addition, the 13 C magic angle spinning (MAS) NMR spectroscopy data of the freshly prepared material was superimposable to that of a previous preparation 15. These results demonstrate the reproducibility of our synthesis methodology.…”

“…The first step was the synthesis of the thiazolium‐based SBA‐15 material 3 (Scheme ). This material was prepared by reaction between the mercaptopropyl‐modified silica SBA‐15 1 and the bisvinylthiazolium salt 2 (Figure S1 to S3) 15. Support 3 has a specific Brunauer–Emmett–Teller (BET) surface area of 116 m 2 g −1 and a cumulative pore volume of 0.14 cm 3 g −1 (Figure S4).…”

“…Such kind of supported ionic‐liquid‐like phase (SILLPs) resulted to be highly efficient, recoverable, and reusable in the Suzuki–Miyaura and in Heck reactions both under batch12 and flow conditions 13. Interestingly, these materials are also able to effectively promote the synthesis of cyclic carbonates,14 ethers,15 or even to act as palladium scavengers 14a. 16 Finally, these SILLPs found application as noncovalent supports for the reversible immobilization of ionic liquid tag‐endowed organocatalysts17 working under a “release and catch” regime 18…”

Advances in Organic and Organic-Inorganic Hybrid Polymeric Supports for Catalytic Applications

“…Furthermore, thiazolium hybrid material 49 displayed higher conversion and selectivity compared to the analogous imidazolium-based material, thus showing that the nature of the N-heterocyclic ring had a determinant impact on the performances of the reaction. The first application of thiazolium-based compounds as catalysts for the etherification reaction of alcohols was reported [38]. Thiazolium hybrid material 49 was prepared by a radical reaction between a mercaptopropyl-modified SBA-15 mesoporous silica and large excess of bis-vinylthiazolium salt 48 (Scheme 21) and successively employed in the etherification reaction of 1-phenylethanol under solvent-free conditions at 160 °C testing different gas phases (oxygen, air, nitrogen and argon).…”